Apparatus for and method of making printing screens



Sept. 2, 1952 A. c. CLUZEL 2,603,750

APPARATUS FOR AND METHOD OF MAKING PRIHTING SCREENS Filed Aug. 25, 1949 4 Sheets-Sheet 1 IN V EN TOR. 14 A 8527' C [10252 A. C. CLUZEL Sept. 2, 1952 4 Sheets-Sheet 2 Filed Aug. 25, 1949 INVENTOR. #45597 C. C L UZEL ATTORNEY N\ M Y r B m w M N h 1 N 3 an m owl F u u my mm I U I III O N mm ck m x N n l E w on m x mm #3 4|. 1 IQI mv o mv I mi N: Q %N\ Rh mwv 6 MW QM. xx wmx wwx Q NN\ w Mm mm\ mQ mum \N\ N Q A. C. CLUZEL Sept. 2, 1952 .APPARAIUS FOR AND METHOD OF MAKING PRINTING SCREENS Filed Aug. 25. 1949 4 Sheets-Sheet :5

INVENTOR.

Patented Sept. 2, 1952 APPARATUS FOR AND METHOD OFMAKING v 1 Pam-TING SCREENS Al -en e, Clu'z'el, niagewe a, lei. Application Au ust 25, 194a Serial No; 1125331 claims.

This invention relates to aqmachin o and a method of afiixingswebzmater a such as ci qt in tightly-stretched condition over a surface of an article. such as a frame, asin the making of silk printing screens: I The machine andmethod o fgthe inyention are useful wherever a somewhat extensible web material ofconsiderable strength must bestretched overjan article such iasa frarnmin suchapplications the invention permits. the ,attainment of tensions in theweb -material which are substantially equal inall directions; The machine and method of the invention iare perhaps best-illustrated in connection with the stretching of silk or the-likecloth web Over a framein the making of printing screens t W 1 The screen stencil ordinarily used in screen stencil printing consists of bolting silkstretched over a wooden frame. on" thislsi-lk the-designto be printed is applied either 'bystencilling r..by photographic means} inthe'latter methodgtlie silk being impregnated with light sensitive mater'ial -on which the patternto be reproduced is projected,- the resulting-pictureentire, screen thenibieing developed. fllheistencikthuspmduced is 'further treated by painting the areawhich is .tOT remain 1 white with-'- some .substance such as gum or shellac .Which FWil-I makethe silk imper'v'ious to the ink used-. :Ilhe stencil is placed in contact with-thesurface'tosbe decorated and a puddle-of ink is-Lscraped from oneuen'd to the other by meansoi a rubber squeegee. forces the: ink, which resembles :ordi'naryhouse paint, through the open areasiof the stencil andtit ad-- heres to the surface beneath. The stencil is then lifted-from the decorated surface and the ink allowed to dry,- after'whlch another color may be appliedirom another stencil, and so on. It can readily be seen frointheabove that-in order to produce first-class printed work it is necessary that the silkrfor'ml'ng 'theyseree'rl be stretched tightly and substantially uniformly as totension inalldirections' finlss' these-conditions are resent the screen will become distorted during use rand itwill-be:-'il'rnpossible to secure registration as to the different colors printed on thefsame' articlefiorn"successivestericils. In the prior art, the sill:- stencil screens have been rormed by stretching tIiejsiIli inanually over the nem raa emng it'to the frame as the stretching pr ceedsl caHy. Itwill be appreciated that by 1 such, it was impossible to s u reens in h h. the-aw re and Weft; threads, remained at rightangles to eaeh other, substantially zthrbiihmitthe 1 area, 9f the i (01. e g-'14s) as a-iranie.

A runner? b e t s if i v fio e d s-min provision of a gna' ohineiin which" thelfroiit 1er 9 th ermine wa after I ulle aw new each other t bu i edge of the web initia y under tension whiohj is equal o at .sl eedlle i pbli "t nsvers ly of the web in other portions thereon Yet another object of the invention res des n the p ov si n 9 amass n n" and s sees sesq t uc a teams t whi h jiS sw e ene re vs ante :an Str tch t6 l i fi 11? ounts H 3 iu h r p net's? the nfidn v d s' in the provision df app ratus of he jlassdescfib'ed i h ch t We Whi e l i fi it ward and side edges, and wardly, is subj eclted toispb n f m ensiqest 1 in l tagtzw th tbsfl' 'lil u e a l e in unscreens-t h -n me 1 VA further object of; the intention resides in th :o.v s n 9f a meter l bd 0 1 ion n thefie gible webinat f H ing it--as a' preliminarystep emanation 619, am I I L v L The a ev and lI QQ LQDJS QES f the in will become more readiI a pafeiit 'in lowingdescription; of preferred ein'b o'd V v e a par tu ami-HQF Qd-Q h lv 1 in the drawings aceornpanying' thespecifi'cation and formingap artthereof Fig. 1 is a view in-planofa referred apparatus the ridl'e fo'r Fig. ,5 is a {ragrnentary yiew in .perspei'c partially invertical section, or eeigeptere th c nitye eamiziiabl f v ei be fie clamp: p I

Fig. 6 is a view in perspective of a finished, covered frame, the silk screen being omitted from a part of such frame; and

Fig. 7 is a view in vertical cross section through the machine shown in Figs. 1, 2, etc., the section being taken along the line 'l-'I in Fig. 1;

In the preferred embodiment of the apparatus shown, there is provided a main frame composed of a first, vertical frame member designated 2, a second vertical frame member designated 4, members 2 and 4 being positioned at the front of the machine, and two parallel vertical frame members 8 and 8 positioned at the rear of the machine. Vertical frame members 2 and 6 are connected together by the bottom tie member H] which rests upon the floor or other support, and vertical frame members'4 and 8 are similarly connected together by the bottom tie member [2. Frame members 2 and 8 are further connected together by the top horizontal tie member 14, and vertical frame members 4 and 8 are similarly connected 'bythe horizontal top tie member l6. Frame members 2 and 4 are further connected by the horizontal intermediate angle member I8, there being a corresponding angle member intermediate the top and bottom ends of the rear frame members 8 and 8. Members i8 and 28 form the support for the platform raising jacks, subsequently to be described. The main frame of the device is completed by the top cross tie memberin the form of an angle iron 22 connecting vertical frame members 2 and 4, a similar connecting angle member 24 connecting therear vertical frame members 6 and 8. i

A rearwardly extending sub-frame, at the right in Figs. 1 and 2, is provided by the horizontally extending upper members of which one is shown at 26 in Fig. 2, member 28 being supported at its outer end by means of the vertical frame support 28. A similar vertical support 29- is provided for the'horizontal member 32 corresponding to member 28 at the other side of the frame, the side frame members being tied together at their bottoms by the angle iron 30.

v The above described rear sub-frame forms the support for the supplyof silk in the form 'of the roll 34 which is supported upon the spindle 36. Spindle 38 in turn is carried by the bearing 38 supported on frame member28 and in the bearing member 40 located on horizontal frame member 32. A crank handle 42 is provided supported on one end of spindle 36,,as shown in Figs. 1 and 4, there being provided on the spindle adjacent the crank the ratchet wheel 44 which coacts with pawl 46 mounted on frame member 32 in such manner as to hold the roll 34 in web tightening condition when the pawl is placed in operative relation with respect to the ratchet wheel, as shown more clearly in Fig. 4. 4

The silk web issuing from roll 34 is designated by the reference character 48. When such web reaches a position in which it lies over the wooden frame to which it is to be attached, and also when it is in attached condition on the frame, it is designated 48'. The web 48 progresses from roll 34 first upwardly over an idler roll 50. Roll 50 is supported at its ends in yokes provided in parallel. spaced, rearwardly directed supporting arms, one of which is positioned at each side of the machine. In Fig. 4 one such arm 52 and the yoke 54 supporting roll 58 are shown.- After running over roll 50, web 48 progresses downwardly beneath the fioatingly mounted vertically guided idler roll 58 disposed in the tank 58. Tank 58 is in the form of a trough positioned between in the vertical squeeze roller housing 82.

and supported by the above mentioned side supporting arms of which one is shown at 52. The vertical sides of the inner surfaces of the paral-- lel supporting arms, which form the ends of the tank, are channeled vertically as shown at 60 on arm 52 (Fig. 4). Such vertical channels in the side arms allow the roll 58 to slide freely and to be guided vertically within such channels. Roll 58 depresses web 48 well beneath the surface of the liquid 51 carried in the preliminary conditioning tank 56. Ordinarily liquid 51 will be water. Web 48 rises from beneath the weighting roll 58 out of the liquid in the tank and into the nip between the bottom and top squeeze rollers 84 and 66, respectively, which are mounted Ad justable screw down members, such as 68, are provided in the housing to vary the compression to which the web is subjected. Rolls 64 and 86 have the function of removing excess moisture from the web and of flattening it as a preliminary to its being stretched overthe' wooden frame.

From the sque'ezerollersweb 48 is led beneath the idler roll 14 which is placed at such level as to insure that the end of the web 'rearwardly of the wooden frame to which it is to be attached lies below the top surface of such frame when the latter is inelevated position, and substantially at the effective clamping level of the front and side clamps, to be described. In initially threading the machine, web 48 is led from roll 34 and is introduced manually over roll 50 and thence between thesqueeze rollers-84 and 86. The shaft 10 of-the' top squeeze roller is provided at one end with an operating hand wheel 12, whereby the squeeze rollers may be operated to feed the web therethrough'. After the web has been fed between the squeeze rollers, the weighting roller 58 may be introduced into the slots in the trough supporting side arms, thereby to depress the web into the liquid in the tank. supported on the horizontal intermediate crosstie'members l8 and 20 are the two parallel inverted Jchannelmember's 18 and 18, as indicated in Figs. 1, 2 and 7. On channel member 16 (Fig: 2')' there isshownsupported a portion of the mechanism forraising orlowering the frame supporting platform of the machine. Four platform raising j acks' are provided, the two jacks or screws 'atthe front being designated 82 and 83, and'the two's'crews at the rear being designated 84 and 85. Each of the screws 82 and 84 (Fig. 2) is supportedon a block which lies on cross member l6. The screws extend freely through openings in blocks 80, screw 82 being threadedly engaged with and supported by the bevel gear 86 which rests in a bearing on block 88, and screw 84 is threadedly engaged with and supported by; the similar bevel gear 88. Gears 86 and 88 are connected together by means of the horizontal shaft 90, each end-of which carries a bevel gear meshing with'the corresponding gear 88 and88. Jack screws 83 and are similarly connected and similarly supported, the screws being connected by the horizontal shaft 98, as indicated in Figs. 1 and '7. Shafts 90 and 98 aregeared together for simultaneous and equal motion, ,whereby. the Jack screws 82, 83, 84 and 85 are all moved in the same direction and in equal amounts. Y The means for connecting and driving shafts 98 and 98 takes the form of a horizontal transverse shaft 98, on one end of which there is connected a gear 94 which meshes with the gear 92, as shown in Fig. 2. A corresponding gear set,

generally designated I08 servesto connect the throughout. the length 01-; theframe I M, and with the tension from beneath the: web by the. elevating platform; that when-applied to the; frame the silk will. have a substantially uniform tension in all directions. After the web. has been subjected to the back tension, as described, its side edges are then clampingly engaged by means of the side clamps I 88 and I80, the prongs: carried bythe lower portion of the clamp, as in the case of the central clamps I20. and the corner clamps I48 and I 50, penetrating the webmaterial and the upper movable clamping member holding it tightly into engagement with the bottom clamping plate. Thereupon crank 228 is turned to move clamps I88 and I90 "apart to subject the web throughout the length of the zone overlying frame H4 to substantial transverse tension. Usually clamps I88 and I90 are moved apart a distance substantially equal to that which clamps I48 and I50 were moved apart.

With the cloth thus held and stretched on its forward end, being given a predetermined back tension by means of the ratchet device on the supplyspindle, being engaged'along the side edges thereof and being given a transverse tension by the side clamps I88 and I90, the handle [02 is then turned to raise screws 82 to 85, inclusive, thereby to bring the platform I04 and the frame "4 into engagement with the under side of the portion 48' of the web; The raising of the platform is continued until the upper surfaces of frame I I4 lie somewhat. abovethe bottom surface of the pressingroll Titheeffective level at which the web is clamped on itsside portions by clamps I88 and I90, and the effective line along which it is clamped by the. front. edge engaging clamps I20, I48, I59, I84 and lilc. The amount of tension thereby additionally impartedto the web 48 by reason of upward movement of frame I I4 may be correlated with the. initial tension. transverse to the forward edge thereof, the rearwardly directed tension imposed. by the ratchet and pawl on the supply spindle, and the transverse tension applied by the side clamps. It possible, by thus correlating the various tensions. imparted to the web, to subject the portionfthereof lying above the frame [I4 to tensions which are substantially uniform in all directions therealong.

With the web 43' thus stretched over the frame H4, it is secured to the frame by means such as tacks or, in the;embodiment shown, the staples 2-38 which are applied conveniently by means of ahand held stapling machine, After the web 48 has thusbeen i'lrmlysecured to the frame, the platform I84 of the machine is depressed to relieve the bottom of frame II4 from the platform, after which the back tension on the web is released by release of the pawl 46. The web material 58 isthen cut transversely rearwardly of the framc,after which the forward and side edges of the'web are released from the forward and side edge. engaging. clamps of the machine. The covered frame may then be removed from the machine and the projecting edges of the vweb trimmedtherefrom.

In some instances it will bei'sufiicientto rely only on the tension initiallyappliedto the forward edge of the web, the-back tension and'the transverse tension throughoutthe 'length of the zone overlying the frame which the web is to be attached, to secure the desired tensions in various directions in the web atta 'ched 't'o the frame. -.In such cases necessary only to elevate platform I04 su'flicien'tly 'to bring the upper surface of frame I M int'oicohtact with the .10 underside of: the Web.. Itis usually preferred, however, to add to such tensions as thatresulting from. elevation Of. platform I04 to, a point such as shown in liig.- 7... Such procedure is especially advantageous. when the frame-I M- is: of the type in which the. upperweb engaging surfaces are curved, an inner longitudinal zone of the upper surface of each frame memberbeing higher than the outer edge thereof. With such frame, which, like frame'l I4, above described may be made of materials such as metal-as well as of wood, the application of the web fastening means to the frame at zones outwardly of said inner, high, longitudinal zones is facilitated when the web is pulled downwardly on all sides below the top of the frame.

Whereas forpurposes ofillustration I have shown and described. a preferred embodiment of the apparatus for making printing; screens of the invention, and also a preferred embodiment of the method of making; printing screens, it is to be understood that such apparatus and method are illustrative only and that the invention is capable of considerable variation as to details of construction of the apparatus and application. of the method. The invention is, therefore, defined by the scope. of the claims appended hereto.

I claim as new-the following: i

1. Apparatus for stretching a web of flexible, somewhat extensible, [material preliminary to its attachment across theface of an article, comprising means for holding said, article to be. covered, means for positioning a web of such material, of sufficient length and width to cover the face of the article, substantially in a plane parallel to and spaced from the said face of the article, said lastnamed means comprising means for gripping the opposite corners of one end of the web, means to move such corner gripping means apart to subject such end of the web to tension in a direction transverse to the length of the web, means for gripping the central portion of such end of the web, means for applying a tension to the web. longitudinally thereof over substantially its entire width, means togripfthe side edges of the web throughout the length of the article, and means to advance the article holding means and the stretched web relatively toward each other to contact the surface of the web with the surface of the article to be covered and to subject the web additionally to tension;

2. Apparatus for stretching a web'of flexible,

somewhat extensible, material preliminary to its attachment across the face of an article comprising means for holding said article to be covered, means for holding a roll of Web material, means for feeding web material from the roll, means for positioning a portion of the forward end of the thus fed web material of sufficient' length, and

' width to cover the face of the article, su'bstane tially in a plane spaced'frorn the said faceofthc article, said last named means comprising means for gripping the opposite corners of 'theforward end of the web, means tomove such corner grip ping means apart to .subjectthe forward end of the web to tension in'a direction transverse to the length 'of' the web,'jmeans fol" gripping" the central portion or suchjthus tensioned forward end of the web, means for applyin'ga back ten-- sion to the web longitudinally thereof over sub stantially its entire width, means to grip the side edges of the web throughout thelength of the article and to subject suchizone of the web to tension transversely'thereto, and'means to advance the'article holding means andthe stretched web relatively toward each other to contact the surface of the web with the surface of the article to be covered.

3. Apparatus for stretching a web of flexible, somewhat extensible, material preliminary to its attachment across the face of an'article comprising means for holding said article to be covered, means for holding a roll of web material, means for feeding web material from the roll, means to moisten the thus fed forward portion of the web to condition it for stretching, means for positioning a portion of the forward end of the thus fed web material, of a width to cover the face of the article, substantially in a plane spaced from the said face of the article, said last named means comprising means for gripping the opposite corners of the forward end of the web, means to move such corner gripping means apart to subject the forward end of the web to tension in a direction transverse to the length of the web, means for gripping the central portion of such thus tensioned forward end of the web, means for applying a back tension to the web longitudinally thereof over substantially its entire width, means to grip the side edges of the web throughout the length of the article, means to move the side edge gripping means apart to subject the web to transverse tension throughout said zone, and. means to advance the article holding means and the stretched web relatively toward each other to contact the surface of the web with the surface of the article to be covered.

4. Apparatus for stretching a web of flexible, somewhat extensible, material preliminary to its attachment across the face of an article comprising an upstanding open framework of genorally rectangular horizontal section, said framework incorporating means for feeding a web of the aforesaid material across the top of the framework longitudinally thereof, the framework having a vertical opening therethrough of such size and shape as freely to accommodate vertical passage therethrough of the article, the framework having at the top thereof spaced parallel horizontal clamps for engaging the side edges of the web, the framework further having at its top front portion a clamp for engaging the central portion of the forward end of the web, and, at the sides of such last named. clamp, laterally movable clamps for engaging the forward corners of the web, means simultaneously and selectively to move said corner engaging clamps toward or away from each other, whereby the forward end of the web may be subjected to tension in a direction transverse to the length of the web, means for supporting the article within the vertical opening in the framework of the apparatus, and means for selectively raising or lowering the article supporting means, whereby the article may be raised into contact with the underside of the stretched portion of the web to subject such portion to predetermined tensions in all directions therealong.

5. Apparatus for stretching a web of flexible, somewhat extensible, material such as silk cloth or the like preliminary to its attachment across the face of an open, box-like screen frame, comprising an upstanding open framework of generally rectangular horizontal section, said framework incorporating supporting means on the rear of the frame for supporting a roll of web material, means for feeding from said roll the forward end of the aforesaid material across the top of the framework longitudinally thereof, the framework having a vertical opening therethrough of such size and shape as freely to accommodate vertical. passage therethrough of the screen 12 frame, the framework having at the top thereof spaced parallel horizontal clamps for engaging the side edges of the web, the framework further having at its top front portion a clamp for'engaging the central portion of the forward edge of the web, and, at the side of such last named clamp, laterally movable clamps for engaging the forward corners of the web, means simultaneously and selectively to move said corner engaging clamps toward or away from each other, whereby the forward end of the web may be sub- J'ected to tension in a direction transverse to the length of the web, means for moving the side edge engaging clamps apart, means for subjecting the web to back tension longitudinally thereof, means for supporting the screen frame within the vertical opening in the framework of the apparatus, andmeans for selectively raising or lowering the screen frame Supporting means, whereby the screen frame may be raisedinto contact with the underside of the stretched portion of the web.

6. Apparatus for stretching a web of flexible, somewhat extensible. material such as silk cloth or the like preliminary to its attachment across the face of an open, box-like screen frame, comprising an upstanding open framework of generally rectangular horizontal section, said framework having at the rear thereof means for supporting a roll of such web material, means supported on the framework for feeding web material from such roll across the top of the framework longitudinally thereof, the framework having a vertical opening therethrough of such size and shape asfreely to accommodate vertical passage therethrough of the screen frame, the framework having at its top longitudinally extending spaced parallel side clamps bordering the vertical opening in the framework on both sides thereof, means mounting suchside clamps for movement on the framework toward" and away from each other, means simultaneously selectively to adjust the side clamps toward or away from each other, the framework having at its top front portion an elongated clamp for engaging the central portion of the forward edge of the web, a web corner engaging clamp'mounted on the framework at each upper forward corner thereof, means simultaneously and selectively to move said corner engaging clamps toward or away from each other, whereby the forward end of the web may be subjected to tension in a direction trans-verse to the length of the web, means for subjecting the web to back tension longitudinally thereof, means for supporting the screen frame within the vertical opening in the framework of the apparatus, and means for selectively raising or lowering the screen frame supporting means, whereby the screen frame may be raised into contact with the underside of the stretched portion of the web. 7. Themethod of stretching a web of flexible material as a preliminary to its attachment to an article so as to lie substantially in a plane thereon which comprises positioning substantially in a plane a portion of such web material which is at least of sufficient length and width to cover the desired surface ofithe article, applying tension substantially, fromicorner to corner to a first end of such portion of theweb in a direction transverse to the lengththereof, clamping the central portion of the thus tensioned first end of the web, applying a tension to the web longitudinally thereof over substantially its entire width, grip-- ping the side edges of the thus tensioned web over substantially the full length of the aforesaid portion, and relatively advancing the article and thus gripped and tensioned portion of the web toward each other in a direction generally normal to said stretched portion of the web, whereby to place the article firmly in contact with the web over the area of the former to be covered by the web.

8. The method of attaching a web of flexible material such as silk or the like to a box-like frame so as to form a printing screen lying substantially in a plane thereon, which comprises the following steps in the order named: positioning substantially in a plane the forward portion of a continuous web of such material, such portion being at least of sufficient length and width to cover the desired surface of the frame, applying tension substantially from corner to corner to the forward end of such portion of the web in a direction transverse to the length thereof, clamping the central portion of the forward end of the web, applying a. back tension to the web longitudinally thereof over substantially its entire width, gripping the side edges of the web over substantially the full length of the aforesaid portion, pulling the gripped side edges of said portion away from each other to subject such portion to transverse tension, relatively advancing the frame and thus gripped and tensioned portion of the web toward each other in a direction generally normal to said portion of the web, whereby to place the frame firmly in contact with the web over the area of the former to be covered by the web.

9. The method of attaching a web of strong, flexible, somewhat extensible material across an open face of a frame which comprises the following steps: positioning the frame to be covered in a predetermined position, positioning a web of such material so that at least a portion thereof of a length exceeding the length of the frame at its forward end lies substantially in a plane parallel to and spaced from the juxtaposed surfaces of the frame, thoroughly moistening the web so as to condition it for stretching, the web being of a width exceeding the width of the frame, applying a predetermined tension substantially from corner to corner to one end of the web in a direction transverse to the length thereof, gripping the central portion of the thus tensioned forward end of the web over substantially its entire length, applying a predetermined tension to the web longitudinally thereof over substantially its entire width, gripping the side edges of the web over substantially the full length of the portion thereof lying over the frame, pulling the gripped side edges of said portion away from each other to subject such portion to transverse tension, moving the frame in a direction normal to the stretched web to bring the surfaces of the frame into contact with the adjacent side of the stretched portion of the web, and fastening the webto the surfaces of the frame with which it is in contact.

10. The method of attaching a web of strong, flexible, somewhat extensible material across an open face of a frame which comprises the following steps in the order named: positioning the frame to be covered in a predetermined position, feeding the forward end of a continuous web of such material from a supply roll so that a portion thereof of a length exceeding the length of the frame at its forward end lies substantially in a plane parallel to and spaced from the juxtaposed surfaces of the frame, in a portion of the path of feeding of the web thoroughly moistening the web so as to condition it for stretching, the web being of a width exceeding the width of the frame, applying a predetermined tension substantially from comer to corner tothe forward end of the web in a direction transverse to the length thereof, gripping the central portion of the forward end of the web over substantially its entire length, applying a predetermined back tension to the web longitudinally thereof over substantially its entire width, gripping the side edges of the web over substantially the full length of the portion thereof lying over the frame, moving the side edges of the web away from each other and laterally from the vertical longitudinal planes in which they lay before being gripped to subject such portion of the web to transverse tension, moving the frame in a direction normal to the stretched web to bring the surfaces of the frame into contact with the adjacent side of the stretched portion of the web, continuing the moving of the frame to subject the stretched portion of the web to an additional predetermined tension in all directions, and fastening the web to the upper surfaces of the, frame.

ALBERT C. CLUZEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 159,696 Magall et a1 Feb. 9, 1875 I 173,720 Guerln Feb. 22, 1876 292,368 Sager Jan. 22, 1884 308,081 Lodge et al Nov. 18, 1884 331,325 Plummer Dec. 1, 1885 371,038 Davis Oct. 4, 1887 885,549 Van Duzee Apr. 21, 1908 1,311,653 Koepp July 29, 1919 1,360,377 Drange Nov. 30, 1920 1,653,919 Miller Dec. 27, 1927 2,036,787 Zabriskie Apr. 7, 1936 2,194,551 Holman Mar. 26, 1940 FOREIGN PATENTS Number Country Date 229,352 Great Britain June 16, 1926 

